V/Q scan

V/Q (ventilation/perfusion) scan is a scintigraphic examination of the lung that evaluates pulmonary vasculature perfusion and segmental bronchoalveolar tree ventilation.

A chest x-ray should be reviewed prior to lung scintigraphy 2 as there are other causes of perfusion defects such as atelectasis

The ventilation scan performed using radio-isotope labeled aerosols like technetium-99m DTPA delivered to the patient through a non-rebreathing mask, with the patient supine. The micro-aerosol particles are small enough to reach the distal tracheobronchial tree and reflect regional ventilation 1. The patient is then imaged in the upright position in three phases: initial breath, equilibrium and washout.

The perfusion lung scan involves injecting Tc-99m MAA intravenously in the supine position. The MAA particles are just small enough to get lodged in the pre-capillary arterioles. A high resolution, large field of view gamma camera is used to image the lungs.

Modified PIOPED criteria can be used to determine the probability of a PE on a V/Q scan. For the diagnosis of PE, a V/Q scan has a reported sensitivity of 77.4% and specificity of 97.7% when compared to CT pulmonary angiography (CTPA) or digital subtraction angiography (DSA) 3.

A normal ventilation scan (even distribution of radionuclide throughout the lung fields) with multiple, bilateral perfusion defects are the classical findings of pulmonary embolism 1.

Causes of ventilation/perfusion mismatch include:

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Article information

rID: 46829
System: Chest
Section: Radiography
Synonyms or Alternate Spellings:
  • VQ scans
  • VQ scan
  • Lung scintigraphy
  • Ventilation/perfusion scan

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Cases and figures

  • Case 1: normal V/Q scan
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  • Case 2: pulmonary embolism
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